Trying to fix the shapely compile error issue that I (and the ocrd_all CI encounter with python 3.8.

For Python <= 3.8:

• Use numpy >= 1.19.3 for the build environment
• Use shapely <= 2.0.1 for the runtime environment (for me the compile errors started with that patch)

For Python > 3.9:

• Use oldest-supported-numpy for the build environment
• Use the most recent shapely for the runtime environment

This seems to work but I am not sure I understand the ramifications of the build requirements and wheter oldest-supported-numpy is deprecated now, so feedback welcome.